The inverter has a forward signal, but the frequency is always zero. What should I do?

Fault phenomenon:

After the inverter is powered on, start the inverter and connect the forward terminal to the common terminal! The inverter RUN light is on! After the user has repeatedly set the inverter running frequency through the human-machine interface, the inverter has no response and the frequency is always zero!

The frequency of the inverter has been set by the external terminal. This inverter controls the motor of the traction machine. Because our factory produces pipes, we need a motor to pull the pipes! The combination of the inverter and the motor is called a traction machine! The inverter is used to drive these two motors.

The frequency of the inverter is written into the PLC by the user through the human-machine interface (this PLC is Siemens S7-200);

Then the PLC gives the frequency to the inverter! The traction speed setting on the human-machine interface refers to the frequency given to this inverter!

When the user writes the required speed into the PLC through the human-machine interface, the PLC expansion module EM232 (analog output module) outputs a voltage of 0V to 10V to set the frequency for our inverter! EM232 module picture)

The EM232 module is an analog output module! The terminals are marked with M0, V0, I0, M1, V1, I1. These are the analog output terminals. If the output you want is a voltage signal, connect M0, V0, and M1, V1. If the output is a current signal, connect M0, I0, and M1, I1. M is the common terminal, V represents voltage, I represents current, and the 0, 1 at the end represents the channel number.

Look at the functions of each terminal of the inverter:

Inverter terminal (AI1) AI is the abbreviation of Analog input, 1 represents channel 1! So how do you connect the EM232 module to the inverter? I have drawn a circuit diagram for you.

According to the speed set by the user, the EM232 module's terminals M0 and V0 will output a voltage of 0V to 10V, which will be transmitted to the inverter analog input terminals GND and AI1. The inverter changes the frequency and sets the frequency by obtaining the voltage on the GND and AI1 terminals!

Now that we have explained to you the working principle of this device, let's deal with this problem!

After setting the speed on the human-machine interface, I used a multimeter to measure the inverter terminals, GND, AI1, to see if there was a DC voltage. The multimeter showed zero, no voltage! At first, I thought that the wires from terminal (EM232 module) M0 to (inverter terminal) GND and (EM232 module) V0 to (inverter terminal) AI1 might be broken, resulting in no voltage!

In order to rule out the possibility of a broken wire, after setting the speed on the human-machine interface, I used a multimeter to measure whether there was voltage output at the terminals M0 and V0 of the EM232 module! The measured voltage was 0V, which also ruled out the possibility of a broken wire! (Due to the lighting problem at the time of taking pictures, I could only simulate it for you)

Since there was no problem with the circuit, I suspected that the EM232 analog output module was broken, so I removed the module. Then I removed a good EM232 module from another machine and installed it! After installing it and testing the machine, I found that there was voltage at the inverter terminals GND and AI1! This proves that the EM232 module has voltage output! At this time, there is frequency on the inverter and the traction motor has started to rotate!

After replacing the EM232 module, the fault was eliminated and the equipment operated normally! The main reason for the equipment failure was that the EM232 module was damaged and there was no voltage output!